A reduced wood pyrolysis mechanism for evaluating solid and gas phase parameters

A reduced wood pyrolysis mechanism comprising of three parallel, first-order reactions was developed to model solid phase heat flow and gas phase combustion parameters. To this end, simultaneous thermal analyzer (STA) studies on a mixed hardwood sawdust sample were conducted for different heating rates (5, 10, and 20 K/min). A nonlinear least-squares model-fitting algorithm was used to extract the Arrhenius kinetic parameters from these experiments. Gaseous species mass flow rates at 1 K/min and 5 K/min were measured by a gas chromatograph (GC) coupled with the STA. The concept of volatile fractions was introduced to correlate the species mass flow rates to the pseudo-component (hemicellulose, cellulose, and lignin) mass loss rates. Sensible specific heats of individual pseudo-components and char were found by using their mass fractions and a progress variable for the degradation. Using the kinetic parameters, gas phase mass fractions, and sensible specific heats, the heats of decomposition of the pseudo-components were evaluated. These parameters formed the inputs of a solid phase heat flow model. This solid phase model was validated against differential scanning calorimetry (DSC) data. The gas phase composition generated by the reduced mechanism was validated against micro-combustion calorimeter (MCC) experiments at different heating rates. The proposed mechanism can be used in wood combustion studies wherein the solid phase heat flow and gas phase combustion processes are coupled. Furthermore, this methodology can be extended to the degradation of any composite material.